1. Field of the Invention
The present invention relates to a protective element for electronic circuits.
2. Description of Related Art
Many electronic circuits and components are supplied with power from a battery or an accumulator. In many applications, it is possible that the battery or the accumulator may be connected to the electronic circuit with incorrect polarity. In this case, the positive pole of the battery is unintentionally applied to the negative terminal of the circuit and the negative pole is applied to the positive terminal. This procedure is referred to as polarity reversal. For example, the accumulator of a motor vehicle may unintentionally be connected the wrong way around in the event of maintenance or repair work. High currents may thus flow through the connected electronic circuits and damage them. A pn-diode, which is inserted between the accumulator and the electronic circuit, may be used as a corrective measure. If the battery is connected correctly, current flows through the diode into the connected electronics. In the event of a polarity reversal, the diode prevents a current flow.
The electronic circuits and components are typically additionally protected against overvoltages, which may occur during operation of a motor vehicle, for example. Thus, for example, positive and negative interfering voltages or overvoltages may occur in a motor vehicle. For example, in the event of sudden load changes or shutdowns of the motor vehicle generator, positive voltages up to approximately 90 V may be generated in a period of time up to approximately 400 ms. Therefore, an additional Zener or Z diode is frequently used for voltage limitation to protect the electronics. A typical protective system, which may also be integrated into a semiconductor, is shown in FIG. 1. Such a protective element contains a polarity reversal protection diode D and a Z diode Z for the overvoltage protection. It is connected between the power supply, i.e., battery B or accumulator, and electronics E. Terminal A1 is connected to battery B or the voltage supply and terminal A2 is connected to electronics E. A3 is connected to ground. The voltage drop of approximately 0.8 V-1 V, which drops via polarity reversal protection diode D depending on the current intensity, is disadvantageous. In addition to the power loss occurring in this case, the voltage supplied by the battery is also reduced by this amount.